The primary objective of these studies is to identify the heterogeneous types of collagen in lung parenchyma. Studies have shown that the interstitial collagens of the parenchyma are composed of two types: Type I and Type III. Type I is the thick fibrillar that is noncompliant. Type III collagen are the loose, randomly arranged fibrils that are probably more compliant. Studies are ongoing to quantitate these collagen types in the parenchyma of normal animal and human lung in health and disease. Since the mechanical properties of lung are critically dependent on the types of collagen comprising it, the heterogeneity of lung collagen is a critically important determinant of lung function. BIBLIOGRAPHIC REFERENCES: Hance, A.J., Bradley, K. and Crystal, R.G. Lung Collagen Heterogeneity. Synthesis of Type I and Type III Collagen by Rabbit and Human Lung Cells in Culture. J. Clin. Invest., 57, 102-111, 1976. Hance, A.J., Horwitz, A.L., Cowan, M.J., Elson, N.A., Collins, J.F., Bienkowski, R.S., Bradley, K.H., McConnell-Breul, S., Wagner, W.M., and Crystal, R.G. Biochemical Approaches to the Investigation of Fibrotic Lung Disease. Chest, 69 (Suppl.), 257-261, 1976.